For example, a direction indication device as illustrated in FIG. 8 is known as a direction indication device for a motorcycle. The direction indication device includes a diode D101, a capacitor C101, a direction indication switch SW, a left-side direction indication lamp 102L, a right-side direction indication lamp 102R, an internal power source 103, an oscillator 104a, a buffer 104b, an N-type MOS transistor NM101, a comparator COMP101 for wire disconnection detection, and a current detection resistor R101. The left-side direction indication lamp 102L has a left-front-side bulb 102LF and a left-rear-side bulb 102LR which are connected to each other in parallel. The right-side direction indication lamp 102R has a right-front-side bulb 102RF and a right-rear-side bulb 102RR which are connected to each other in parallel. The diode D101 and the capacitor C101 function as a bootstrap circuit.
Operation of the direction indication device will be described. For example, when the direction indication switch SW is ON to the side of an L terminal, a terminal on the negative side of the capacitor C101 is grounded via the bulbs 102LF and 102 LR. Thus, current from a battery B flows through the capacitor C101 via the diode D101, and thus the capacitor C101 is charged. Accordingly, the internal power source 103, the oscillator 104a, a buffer 104b and the comparator COMP101, to which an internal power supply voltage Vcc is supplied from a terminal on the positive side of the capacitor C101, and to which a reference voltage VS is supplied from the terminal on the negative side, are activated. The internal power source 103 generates a voltage V101 or the like supplied to the comparator COMP101.
The activated oscillator 104a generates an oscillation pulse signal. The buffer 104b outputs the pulse signal by buffering the oscillation pulse signal. The N-type MOS transistor NM101 causes a drive current, a magnitude of the drive current corresponding to the amplitude of a pulse signal supplied to a gate, to flow from a drain to which the power supply voltage VDD is supplied, to a source. The drive current flows through the bulbs 102LF and 102LR of the direction indication lamp 102L via the current detection resistance R101 and the direction indication switch SW. Accordingly, the direction indication lamp 102L blinks at a period of the oscillation pulse signal.
In the direction indication device, in a case where any one of the front-side and rear-side bulbs 102 LF and 102 RF is wire-disconnected, the drive current is reduced. Consequently, the comparator COMP101 detecting an increase in the power supply voltage VDD resulting from a decrease in the drive current controls the oscillator 104a and thus causes a period of the oscillation pulse signal to be changed. Accordingly, since a blinking period of the direction indication lamp 102L is changed, the wire disconnection of the bulb may be reported to a user or the like.
Furthermore, the direction indication switch SW is a mechanical switch. Thus, when a cheap component with low waterproof performance is used as the direction indication switch SW, the leak current may flow via water even though the direction indication switch SW is OFF. Then, the direction indication device starts to work due to the leak current. However, because the leak current is smaller than the current necessary to light the bulbs 102LF, 102LR, 102RF, and 102RR, the blinking of the direction indication lamps 102L and 102R is not visually recognized, and this is not a problem in practice.
The direction indication device as disclosed in JP 1-90831 A is also known as a device similar to the direction indication device described above.
Incidentally, it is desired that an LED element is used as the direction indication lamps 102L and 102R of the direction indication device, instead of a bulb.
However, because the LED element is remarkably great in luminance efficiency compared with the bulb, there is a concern of the LED element emitting light to a degree of visually recognizable brightness due to the leak current from the direction indication switch SW. That is, regardless of the direction indication switch SW being OFF, there is a concern of the direction indication lamps 102L and 102R blinking.